[gradsusr] problem in eof function

[kombo kai]

Hi dear grads users
I am running the eof function to get the principal component analysis for the u wind at 850hPa level for the region as defined in the script example below, but stll I am getting error in eudeof function
example script
sdfopen 850uwnd.nc
set lon -70 120
set lat -45 45
set time sep1980 sep2010
run eof - o swio -neof 20 -npc 10 -nper 30 u85*cos(lat*3.14/180)
when I run script I am getting the following errors
invalid operand eofudf
Display error 
invalid expressions  eofudf(85, ----------)
how can fix this ? any sugestion or  directives
regards
kaikombo



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